Macromolecules 1992,%,6739-6743
6739
New Activating Agents for the Anionic Polymerization of Lactams N. Mougin, P. Rempp, and Y. Gnanou*tt Znstitut Charles Sadron, CRM/EAHP, 6,rue Boussingault, 67083 Strasbourg Cbdex, France Received February 19, 1992; Revised Manuscript Received August 3, 1992 ABSTRACT Metal dialkylaluminumhydrides and strongbases (NaH, BuLi)associated with reducingagents [(alkyl)zAlH,(alkyl)*H, RMgBr] are shown to form a new class of activating agents for the anionic polymerizationof lactams. Upon treating caprolactam(EL) with these new activatingagents,active species of reduced nucleophilicity,8~ comparedto the mere caprolactamateanions,are obtained. Once deprotonated, the monomer undergoes a reduction by these activating agents at ita carbonyl position. These active species behave very similarly to sodium 2-(dialkoxyaluminoxy)-l-azacycloheptane,a salt obtained upon reacting tCL with sodium dialkoxyaluminum hydride (NaAlH2(0R)z)and whose contribution to the polymerization of lactams has been thoroughly investigated.' From these similarities,it is suggested that the mechanism of polymerization which occurs in the presence of these new activating agents should be very much the same as that discovered for NaAlH2(0R)2.
I. Introduction In a recent study, Veith and Cohen2 found that the reactive salts, obtained upon treating e-caprolactam (cCL) with lithium dialkoxyaluminum hydride, are less nucleophilic than the classical lactamate anions generated by deprotonation of eCL with a strong base. Gnanou,Cohen, and their co-workers' described the mechanism of lactam polymerization in the presence of such activating agents, i.e., metal dialkoxyaluminumhydrides, and showed that it is quite different from the classical "activated monomer" mechanism. In the latter case, the active species is the lactamate anion and it is obtained upon deprotonation of the monomer by a strong base (NaH, LiAlH4, BuLi). Initiation results from the attack of this lactamate anion onto a N-substituted lactam compound (acyllactam), intentionally introduced in the reaction medium to trigger the polymerization. A new acyllactam function is formed in this way at the chain end. Each propagation step then involves the transfer of the negative charge carried by the chain to a fresh monomer and the subsequent addition of activated monomer to the terminal acyllactam f ~ n c t i o n . ~ When metal dialkoxyaluminum hydrides are employed as activating agents, the nucleophilic species produced is no longer the classical lactamate anion and a new mechanism of polymerization has been proposed' to account for the results obtained (Scheme I). We showed that the reaction of e-caprolactam (cCL; 1) with sodium dialkoxyaluminum hydride (2) gives rise to the sodium salt of 2-(dialkoxyaluminoxy)-l-azacycloheptane(5). The formationofthe latter compound occura in two steps: first, deprotonation of cCL at its amide position and, second, reduction of its carbonyl function by the dialkoxyaluminum hydride formed during the previous step. For the initiation to occur, the presence of N-acylated lactam is required, as in the classical case. The attack and the addition of the nucleophilic species (5) results in the formation of a 2-(dialkoxyaluminoxy)-l-azacycloheptane group (6) at the chain end. The activation process of a fresh monomer, which follows the previous addition, is more complex than in the classical scheme. After the transfer of the negative charge carried by the penultimate unit to the monomer, the reduction of the lactamate anion immediately ensues by displacement of both the hydride and dialkoxyaluminum groupsfrom the terminal function
* To whom correspondence should be addressed. t
Current addreee: LCPO-ENSCPB, Universit4 Bordeaux, 361
C o w de la Libhation, 33405 Talena CMex, France.
Scheme I 1st Step : * Metalation of Monomer
*
Reduction ofcarbonyl
mN-Cy -OAl(OR)z
Na
(5)
2nd Step: * Initiation
-
3rd Step : * Exchange I'roton versus Negative Charge
HN-CO
u
*
Group'I'ransfer
mn
Na
N-CO, .'I
-CO-NH
uCO-N- d - 6
4th Step : * Propagation
-CO-NH
J
..
0-N-CO
v
t
mB
Na
(6). Upon this process the active species (S),identified above as resulting from the reaction of NaAlH2(0R)2 with cCL, is restored, while an acyllactam function is re-formed at the chain end. The way is thus paved for a new propagation step which will occur by addition of 5 onto the electrophilic acyllactam function. Such a concerted transfer of a group as large as dialkoxyaluminum and of hydride resembles the Meerwein-Ponndorf reduction, which also involves the displacementof both hydride and aluminum derivatives. k o m the mechanism outlined above, it can be w n that the monomer has to be activated before each propagation step. It therefore shares with the classical mechanism the
0 1992 American Chemical Society
6740 Mougin et al.
Macromolecules, Vol. 25, No. 25, 1992
Table I Characteristics of PDMS Chains after a Contact Period of 2 h with Various Lactam Salts at 80 O C
PDMS after a given period active species
initial PDMS
Na+-N-CO
Mn = 5037, M, = 6000,
HN-CO + LiAlHz(O-t-Bu),
Mn = 3800,
U
I = 1.18 W
M, = 4200, I = 1.1
HN-CO + N ~ A ~ H ~ ( O C H ~ C H Z O C H ~M,, ) ~= 3400, U M, = 3800, I = 1.10 M, = 5000, HN-CO + LiAlH[OCH(CH3)21,” W M, = 5900, I = 1.18 HN-CO + NaAlHzEk Mn = 3850, v M , = 4400,
NaN-CO + HB[CH(CH,)CH(CH3)Jz (stoichiometry)
”
NaN-CO + HB[CH(CH3)CH(CH3)Zl, U (excess) LiN-CO + tCH3),CHCH2MgBr U
BrMgN-CO U
I = 1.14 M , = 5030, M, = 6000, I = 1.18 M,,= 3800, M, = 4400, I = 1.14 M , = 4800, M , = 5400, I = 1.12 M , = 3400, M, = 3770, I = 1.10 M, = 3400, M, = 3800, I = 1.10
LiAlH4 + LiAl[OCH(CH3)214.* Contact period = 2 h
of contact with the active species t = 2 h + 1hb t=2h
M,,= 700, M, = 4800, I = 6.9 Mn = 3600, M, = 4600, I = 1.27, small
80%
shoulder is the small M W domain M. = 3100, M, = 3550, I = 1.17 M,,= 2400, M, = 3600, I = 1.53 M , = 3500, M , = 4200, I = 1.2 M,,= 4830, M, = 5600, I = 1.16 M, = 1800, M, = 4000, I = 2.11
M, = 4600, M, = 4900, I = 1.3
M,,= 3500, M, = 3900, I = 1.11
M,,= 3430, M, = 3800,
convn of cCL lesa than 10%
80%
no polymn 80% 25% 58%
Mn = 5150, M, = 5800,
85%
I = 1.12
Mn = 3200, M, = 3600,
84%
I = 1.10
79%
I = 1.1
+ 1 h of tCL polymerization.
same basic feature. However, the two mechanisms differ on two crucial points, namely, on the type of active species formed and on the activation process of fresh monomers throughout the polymerization. In addition to these specificities, Veith and Cohen2found that the two kinds of active species behave quite differently toward the electrophilicS i 4 bonds of poly(dimethylsiloxane)(PDMS) chains. The mere lactamate anion aggressivelyreacts with siloxanebonds, giving rise to silanolate anions, which were found to be detrimental to lactam polymerization (see run 1in Table I). In contrast, the sodium salt of 2-(dialkoxya1uminoxy)-1-azacycloheptaneformed upon using sodium dialkoxyaluminum hydride is totally inert toward PDMS and yet able to bring about the polymerization of lactams1s2(see runs 2 and 3 in Table I). This unique feature prompted us to develop new activatingagentswhich could functiontoward tCL as metal dialkoxyaluminum hydrides and exhibit the same selectivity. The key idea upon which the current investigation is based is to utilize compounds able first to deprotonate cCL and then to reduce its carbonyl function. We did not undertake a mechanistic study similar to our recent investigation on the behavior of 5, nor did we endeavor to identify the active species formed upon treating each of the activating agents with rCL. Instead, we have merely exposedthe various active speciesto PDMS chains and examined their subsequent ability to induce lactam polymerization. Upon checking the integrity of the PDMS and determining the conversion of cCL, we should be able to establish which of the new activating agents would work as metal dialkoxyaluminum hydrides. The PDMS merely serves to assess the nucleophilicity of the active species formed. If a given nucleophilic species,
obtained upon using one of the new activating agents, is found inert toward PDMS and yet able to bring about polymerization of lactams, one could conclude that it presumably possesses a structure similar to 5, a salt of 2-(dialkoxyaluminoxy)-l-azacycloheptane.The mechanism of polymerization would be in this event much the same as that found for 5. 11. Selection of New Activating Agents for the Anionic Polymerization of Lactams We have evidenced the selectivity of sodium bis(2methoxyethoxy)dihydroaluminate in ita reaction with eCL and stressedthe role of the two hydrides.’ As a nucleophilic reagent,NaAlHAOR)2 attacks the weakly acidicN-H bond of eCL and generates both a caprolactamate anion and dialkoxyaluminumhydride. The latter compound, ae an electrophile(Lewisacid),preferentiallyreade with centers exhibiting high electron density and therefore serve8 to reduce the carbonyl function of the activated monomer. With metal aluminum derivatives containing either more or less Al-H bonds (LiAlH4 or LiAlH(OR)3,respectively) than the dialkoxydihydroaluminatesmentioned above, it was shown that the product obtained upon reaction with cCL is the lactamate anion.2 While examining the various compounds which could function toward eCL as did 2, we came to consider two possible approaches: (a) To make use of alkali-metal aluminate or borane complexes possessing two metal hydrogen bonds. Besides metal dialkoxyaluminum hydrides, whose behavior is known, dialkoxy- or dialkyl-substituted metal borohydrides and dialkyl-substituted metal aluminohydridesfall in these two families of reducing agents. Unfortunately,
Anionic Polymerization of Lactams 6741
Macromolecules, Vol. 25, No.25, 1992
neither metal dialkoxydihydroborane nor the dialkoxy derivative was commercially available at the time of our investigation. Sodtam dialkyldihydroaluminate was thus the only activatingagent of this categoryto be investigated. (b) To associate a strong base with a compound capable of reducing the carbonyl function of lactams. The role of the base (BuLi or NaH) is merely to deprotonate the lactam, while the function of the reducing agent is to give rise to a structure similar to 5. Dialkylaluminumhydride, disiamylborane-known for its selectivity toward substituted amides-and Grignard reagents possessing a hydrogen on their @ carbon atom are the three reagents used to reduce the activated monomer.
111. Results and Discussion It is important that the reduction of activated monomer be complete before introducing PDMS. Otherwise, some lactamate anions may be left in the reaction medium and could inducethe degradation of PDMS chains. It is equally essential that this reduction be selective-no further reduction-and occurred accordingto a scheme similar to that established for metal dialkoxyaluminum hydrides. For these various reasons, the experimental conditions chosen to generate the active species differ from one activating agent to another. On the other hand, the procedure followed afterward is essentially the same, regardless of the active species obtained. Then, fresh monomer and a PDMS sample of sharp and known molecular weight distribution are introduced into the reaction medium. After a 2-h stirring at 80 "C, an aliquot is sampled out and washed with MeOH;the PDMS isolated in this way is analyzed by GPC. Subsequently, undecylenoyl caprolactam, whose concentration is the same for all runs, is introduced in the reaction medium to trigger lactam propagation. The polymerization is systematically stopped after 1h of reaction at 80 "C and the conversion of eCL determined. The PDMS which has experienced this additional 1 h of lactam polymerization is isolated and characterized by GPC. (a) Sodium Diethyldihydroaluminateas Activating Agent (NaAlH2R2). Addition of sodium diethyldihydroaluminate (2 M solution in toluene) into the flask containing pure molten t-caprolactam is carried out at 80 "C and stopped as soon as the HZevolution, characteristic of monomer deprotonation, ceases. Continuing the addition may provoke a second reduction of the activated monomer. The amount of activating agent introduced (4 X 10-3 mol, 2 mL), per mole of eCL present (6.7 X mol, 0.75 g), does not exceed 60%. The reaction is stirred for mol of fresh several hours at 80 OC before 9.3 X monomer (10.5 g) and 6 g of a PDMS sample are introduced. The PDMS isolated after a 2-h exposure to the active species is intact and did not experience any degradation (MWDis unchanged). Then, 4 X molof undecylenoyl caprolactam (0.11 g) is introduced. Conversion of t-caprolactam amounts to a value as high as 80% after 1h of polymerization, which is a remarkable result (Table I). These two features, nondegradation of PDMS and high eCL conversion, do indicate that the active species generated upon reacting eCL with NaAlHz(Et)z behaves very similarly to 5. These results suggest that the lactamate anion is indeed reduced by the AlHRz formed upon monomer deprotonation. Active species of reduced nucleophilicity,as compared to the mere lactamate anion, are obtained. Their structure could be
H
+ - I
El),
NaN-C-0-AI(
v
(b) Lithium Triisopropylhydroaluminateas Activating Agent (LiAlH(OCH(CHs)2)s). Veith and Cohen2 have shown that trialkoxy-substituted lithium aluminum hydrides are unable to give rise, upon reaction with tCL, to a species similar to 5. It was inferred from this observation that two A1-H bonds are needed in the activating agent to generate a structure equivalent to 6. Yet, the reduction of carbonyl functions does not necessarily require the use of a true hydride, such as aluminum or boron hydride. This reduction can for instance be obtained upon reacting the carbonyl function with aluminum triisopropoxide; such a reaction occurs by hydrogen transfer from the carbinolcarbonto the carbonyl and is called Meerwein-Ponndorf reduction4
R'-C
R'
1'
n
e
'H
\ / .Ai
CH,
C
-
'0
I
R'-C-H
I
t (CH&C=O
R
'CH,
We thought of applying this reaction to the reduction of the activated lactam. This could be theoretically possible upon using an activating agent such as LiAlH[OCH(CH3)2]3. After deprotonation of rCL (0.75 g, 6.7 X mol, 5 mL of a 1M THF mol) by the hydride (4 X solution), we expected the reduction of its carbonyl function by the triisopropoxide aluminum group formed during the previous step. The medium is stirred for 5 h at 80 "C, before fresh monomer (9.3 X mol, 10.5 g) and PDMS (6 g) are added. The results obtained are disappointing (Table I). The PDMS exposed for 2 h to the active species is noticeably degraded; as to the polymerization of lactam, triggered after introduction of undecylenoylcaprolactam (4 X lo4 mol, 0.11 g), it resulted in a negligible tCL conversion. The reduction of the activated monomer by AlOCH(CH3)2, which was envisaged, has not occurred. This unexpected result may be due to the peculiar behavior of LiA1H(O-i-Pr)3.5 Indeed, it was shown to disproportionate, as soon as it is formed into lithium aluminum tetraisopropoxide-which precipitates out of the solution-and lithium aluminum hydride (LiAl&).
-
4LiAlH(O-i-Pr), 3LiAl(O-i-Pr), + LiAlH, The latter reagent, which is known to mainly generate lactamate anions upon reacting with ECL, might have played the role of the activating agent in lieu of LiAlH(O-i-Pr)a. This could therefore explain the behavior observed. (e) Association of a Strong Base (NaH) with a ReducingAgent (LewisAcid). Two types of Lewis acids have been tried in association with sodium hydride as deprotonating agent. Bis( 1,t-dimethylpropyl)borane (Disiamylborane). Only 60% of the eCL introduced (0.75 g, 6.7 X mol) can be deprotonated in the experimental conditions chosen, T = 80 "C and in the bulk, with sodium hydride as the activating agent. Further addition of NaH does not give rise to hydrogen evolution. The reaction medium mol of sodium lactamate is thus constituted of 4 X (60% of initial tCL) and of 2.7 X mol of eCL (40% of initial eCL) when disiamylborane is introduced. Addition of the latter compound is carried out at 0 "C; the
Macromolecules, Vol. 25, No.25,1992
6742 Mougin et al,
medium is then stirred overnight at room temperature. mol) and PDMS (6g) are then Fresh monomer (9.3X added. The amount of reducing agent to be used in the first step was found to be of paramount importance. We envisaged two possibilities: (1)To add 1 equiv of lactamate salt, assuming that the mol, 8mL of a 0.5MTHF solution) reducingagent (4X will react exclusively with the carbonyl function of the latter reactive species and stay inert toward the 40% of nonactivated cCL still present. The results obtained clearly indicate that this is not the case. The PDMS (6 g) in contact with the nucleophilic species is indeed slightly degraded; the conversion of cCL (58% ! 1, determined after mol, introduction of undecylenoylcaprolactam (4X 0.11g) and 1 h of heating at 80 "C, is noticeably lower than a would-be active species inert toward PDMS (Table I). It is reasonable to infer from these results that some disiamylborane hydride has been consumed in the deprotonation of tCL, preventing the expected complete reduction of lactamate anion. The residual lactamate anion (2) should be responsible for the degradation of PDMS. (2)Increasing the quantity of disiamylborane (6.7X mol, 13.4mL of a 0.5 M THF solution) brought about dramatic changes. In this second attempt, we did not refer to the concentration of a lactamate salt as previously but to the totalamount of lactam. We thus added 1equiv disiamylborane/l mol of the initial caprolactam. The PDMS exposed to the active species formed in these conditions is intact, and at the same time the cCL conversion determined as above is quite high (85%) (Table I). These results bring an undisputed confirmation to our above statement: due to the loss of some HB(alky1)~in the deprotonation of the monomer present in the reaction medium, it was not possible to achieve a quantitative reduction of lactamate anion. Upon augmenting the amount of HB(alky1)p the reduction of the residual lactamate anion becatbe possible, leading to the quantitative formation of the expected active species whose structure should be + - /
H
CH3
I
NaN-C -0B[CHCH(CH3)&
v
B
This active species of reduced nucleophilicity behaves very similarly to 5 and fully meets our objectives: nondegradation of PDMS and high conversion obtained for eCL. In a separate experiment to further confirm the deprotonation of cCL by HB[CH(CH3CH(CH3)2)32, we have separately examined the behavior of disiamylborane hydride toward pure tCL. Upon adding the Lewis acid to melted tCL, a strong H2 evolution, characteristic of monomer deprotonation, is men, but the reduction of the carbonyl function does not seem to occur. We then checked the ability of disiamylboraneto induce the polymerization of cCL in the presence of acyllactam. Disiamylboron lactamate is found totally inactive, and no polymerization occurs in its presence. It can thus be concluded that the dialkylboron lactam that is formed simultaneously to the reduced amide salt (8) does not harm the polymerization process. Diisobutylaluminum Hydride [(i-Bu)nAlH]. This Lewis acid behaves essentially as disiamylborane. The reduction of the lactamate anion carbonyl should be quantitative, provided no residual cCL is present in the reaction medium. Upon adding an appropriate amount
of diisobutylaluminumhydride (4X le3molof HAl(alltyl)2 for 4 x of tCL), an active species of reduced nucleophilicity is obtained, upon stirring the reaction medium for 5 h at 80 "C. Indeed, it behavea similarly to 5 as far as the inertness toward PDMS is concerned: the latter polymer (6g) which is introduced, in a second step, along with fresh monomer (9.6X mol, 10.85g) remains undamaged. Addition of undecylenoylcaprolactam (4X mol) results, however, in an unexplained rather low tCL conversion. (a) Strong Base Associated with Organomagnesium Compounds. The reduction of amide carbonyls and more generally of ketones by organomagnesium compounds is well-known6 It should therefore be possible to use these reactants to reduce the carbonyl function of lactamate anion, in order to generatea structure equivalent to 5. Attention must, however, be given to the selection of the appropriate Grignard reagents. To obtain a structure similar to 5, which implies the reduction of the carbonyl, we must choose a Grignard reagent possessing a single j3 hydrogen suchas isobutylmagnesium br~mide.~ With such a compound, the reduction of the carbonyl function occurs by hydride transfer, according to the following sixmembered transition state: CH3
I
F H 3
A mere alkylmagnesium bromide would give 1,2 addition, which we do not want. On the other hand, it should be borne in mind that organomagnesium compounds, as nucleophilic reagents, can deprotonate the cyclic lactam and give rise to "caprolactam magnesium bromide". The latter species is known to induce lactam polymerization in the presence of an initiator (acyllactam).* We show (see Table I) that it actually brings about the polymerization of cCL. If one wants to strictly use Grignard reagents as reducing agents, it is therefore of importance that the monomer be first entirely deprotonated by a base. Otherwise, one could have two types of propagation upon polymerizing tCL. The monomer (4X lop3mol, 0.45g) is reacted first with a stoichiometricamount of BuLi (2.5 mL of a 1.6 M solution in hexane), in THF solution at -40 "C for 2 h. Under these conditions only can we be sure that deprotonation of eCL is complete. The solvent is then evaporated and the temperature raised to 80 "C. A stoichiometricamount of isobutyl magnesium bromide (4 X mol, 2 mL of a 2 M solution in diethyl ether) is introduced, and the reduction of the lactamate anion carbonyl is carried out. The reaction medium is stirred at 80 "C for 8 h, before a mol, 10.85 g) and 6 g further amount of tCL (9.6 X of a PDMS sample are added. The active species formed are proven to be inert toward PDMS. The sample which has experienced a 2-h contact with the active species is not degraded as shown by its unaltered MWD. This means that reduction of lithium caprolactamate has occurred as expected, leading to the presumed following structure: ti + -
I
LIN-C-OMgBr
W
Macromolecules, Vol. 25, No. 25, 1992
The new active species does cause tCL polymerization in the presence of undecylenoylcaprolactam (4 X lo-' mol, 0.11 g). The conversion of eCL (84%)isindeed fairly high after 1 h of polymerization. IV. Conclusions In the classical anionic polymerization of lactams, the active species responsiblefor chain growth is the lactamate anion. T h e latter speciesis generated upon deprotonation of the monomer by a strong base such as NaH or BuLi. We introduce in this paper a series of new activating agents which do not function as the above-mentioned bases when they are reacted with lactams. The active species generated upon treating these reagents with lactams are less nucleophilic than the mere lactamate anions, yet they are able to bring about the polymerization of lactams. The behavior of these activating agents toward ladams reminds us of that exhibited by NaA1H2(OR)2,1*2which gives rise to sodium 2-(dialkoxyaluminoxy)-l-azacycloheptane by reaction with &L. Although the structure of the various active species formed has not been characterized, the similarities found between NaAIH2(0R)z and some of the activating agents presented herein suggest that the latter reagents reduce the carbonyl function of activated monomer. The reduced nucleophilicity of some active species may be explained using this argument. V. Experimental Part Monomer. c-Caprolactamis distilled twice under vacuum in the presence of CaH2. The monomer is then freeze-dried prior to ita use. Reagents. Sodium hydride, sodium diethyldihydroaluminate, diisobutylaluminum hydride, and isobutylmagnesium bromide were purchased from Aldrich and used without further purification. Isopropyl alcohol is purified according to the well-knownLund and Bjeruum procedure. The synthesis of undecylenoylcaprolactam is described elsewhere.' Synthesis of Bis( l&dimethylpropyl)borane (Disiamylborane). Bis(l,2-dimethylpropyl)borane (disiamylborane) is prepared by hydroborationof 2-methylene-2-butenewith borane in the ratio of l:Z9 The reaction is carried out in THF at 0 OC. Synthesis of Lithium Triisopropodde Aluminum Hydride. To a solution of LiAlHr mol) in THF (10 mL) are mol of isopropyl alcohol slowly at 0 OC. The added 3 x
Anionic Polymerization of Lactams 6743 medium becomes turbid soon after the beginning of isopropyl alcohol addition, and a precipitate is formed. Synthesisof a cr,t+Bis(trimethyl)ply(dimethylsiloxane) Exhibiting a Narrow Distribution. The best way to obtain such a sample is to resort to the anionic polymerization of hexamethylcyclotrisiloxane (Ds). The polymerization of Ds is initiatedwith BuLi, in benzene solution;propagation occurs upon adding some THF (THF/C& = 1). The polymerization is terminabdwithtrimethylchlorosilane(seeref lofor moredetails). Procedure Ueed To Assess the Nucleophilicity of the Active Species Formed. The synthesis of the various active species is described in the text. We systematically worked with the same molar amount of active species (4 X mol). Once the active species is formed,fresh monomer (generally9.6 X 10-2 mol, 10.86 g), whose amount is calculated to make a ratio [active species] to [cCL] of 4100, and the above-mentioned PDMS (6 g) are introduced. In all cases, the reaction medium is *matroscopically" homogeneous. After a 2-h exposure to the active species at 80 OC, an aliquot is taken off and analyzed by GPC with toluene as eluent. The activator,undecylenoylcaprolactam, is added next; ita molar amount was chosen equal to that of the active species. In the majority of cases, whenever eCL polymerization occurs, the polyamide precipitates out of the medium at low conversion, because of ita tendency to crystallize. Polymerization then proceeds in a heterogeneous medium, stirred at 80 "Cfor an additional 1h. PDMS and the polyamide formed are separated upon washing the medium with THF. Residual monomer can be removed in this way as well. After a thorough drying of the polyamide, the conversion of cCL is obtained. In some cases, the PDMS, which has experienced the 1-h lactam polymerization, has been characterized by GPC.
Acknowledgment. The authors are indebted to Rh8nePoulenc for financial support. References and Notes R. E.; Gnanou, Y. Macromolecules 1992,25 (7), 2004. (2) (a) Veith, C. A.; Cohen, R.E. Polym. R e p r . (Am. Chem. SOC., Diu. Polym. Chem.) 1990,31 (l),42. (b)Veith, C. A,; Cohen, R. E. Makromol. Chem., Macromol. Symp. 1991,42143, 241. (3) Sebenda, J. Comprehensiue Polymer Science; Allen, G., Bevington, J. C., Eds.; Pergamon Press: Oxford, U.K., 1988; Vol. 3, p 511. (4) Moulton, W. N.; Van Atta, R. E.; Ruch, R. R. J. Org. Chem. 1961,26, 290. ( 5 ) Brown, H. C.; McFarlin, R.F. J. Am. Chem. SOC.1958,80,5372. (6) Anteunis, M. J. Org. Chem. 1961,26,4214. (7) Whitmore, F. C. 105th National Meeting of the American Chemical Society,Atlantic City, NJ, 1943. (8) Griehl, W.; Schaaf, S. Makromol. Chem. 1959, 32, 170. (9) Zweifel, G.; Brown, H. C. Org.React. 1963, 13, 1. (10) Gnanou, Y.; Rempp, P. Makromol. Chem. 1988,189, 1997. (1) Mougin, N.; Veith, C. A.; Cohen,
